Mexican authorities said Friday they had found nearly 500 U.S.-bound migrants, more than half of whom were children, hidden in a compound near Mexico City.

Mexico’s National Institute of Immigration officials said 491 migrants were being held in a walled compound near the city of Puebla, next to a route frequented by migrant smugglers, CBS News. report. The newspaper said 277 of the migrants found were children and adolescents, 52 of them unaccompanied. (Related: Record Number of Unaccompanied Immigrant Children Detained by Biden Administration: Report)

The Mexican immigration agency said late Friday that it had found 491 migrants detained on a highway-side property east of Mexico City. https://t.co/Ho5i4zyt1B

— CBS News (@CBSNews) August 5, 2023

Smugglers often hide migrants in places like those found near Puebla until they can be loaded onto buses and trucks and transported to the U.S. border, the newspaper said.

According to a CBS News report, the National Institute for Migration said the migrants in the incident were transferred to headquarters where they were provided with food, water and medical care.

Mexico has recently stepped up its efforts to crack down on illegal immigration, closing an immigration office on its shared border with Guatemala that previously issued temporary permits to travel north. Mexico’s southern neighbors have introduced similar procedures to “stop” illegal immigration.

Despite these efforts, a record 250,000 migrants crossed the Darien Gorge between January and July 2023, surpassing the number of migrants who made dangerous crossings in 2022 as a whole. The population across Colombia and Panama could nearly double by the end of 2023, reaching 400,000. according to UNICEF. UNICEF says many of the migrants are unaccompanied children despite it being one of the world’s most dangerous borders.

Of the 491 migrants found in Mexico, all but six were from Guatemala, the rest from Honduras, according to a CBS News report.